Removing and collecting oil

ABSTRACT

Apparatus is described for the removal and recovery of pollutant oil and the like floating on the surface of a body of water, comprising: means capable of the physical withdrawal of pollutant oil and the like with or without additional water from the water surface to a recovery station on site; means for spraying hot water over such pollutant oil and the like at said recovery station; a receiving tank for the oil/water washings resulting; an oil/water separator/coalescer for separating oil containing a minor quantity of water only from the washings; means for receiving such separated oil; means for recirculating water from said separator/coalescer for heating and further spraying; and means for returning any excess purified water from said separator/coalescer to said body of water. 
     A method for the removal and recovery of oil floating on the surface of a body of water is also described, which method comprises the steps: the physical withdrawal of pollutant oil and the like with or without additional water from the water surface to a recovery station on site; spraying hot water over such pollutant oil and the like at said recovery station; receiving the oil/water washings resulting; separating oil containing only a minor quantity of water from the washings; re-circulating water from which oil has been separated for heating and further spraying; and returning any excess purified water to said body of water.

FIELD OF THE INVENTION

This invention relates to the removal or recovery of oil floating on awater surface.

As will become apparent from the detailed description which follows, aprincipal use (although not necessarily the only use) for methods andapparatus in accordance with the present invention is in clearing up oilspillage which has occurred on the surface of the sea, rivers, inlandwaterways, gravel pits, etc., particularly where rapid removal of an oilslick has to be accomplished in order to avoid pollution and ecologicaldamage.

BACKGROUND OF THE INVENTION

In recent years with increasing interest and concern with environmentalproblems, numerous systems have been proposed for removing andcollecting oil floating on water surfaces. A principal disadvantagewhich has become apparent on seeking to put the numerous prior proposalsinto practice has been their marked inability to work effectively in arough sea. This is especially so in the case of suction devices, wherewave motion results in the device ingesting large quantities of seawater along with the oil, rendering the rate of oil removalunsatisfactorily slow and also resulting in a substantial volume of oiland sea water which must be retained on board a vessel for subsequentprocessing.

Of course, numerous proposals have been made for separating oil andwater, but such arrangements are inherently bulky and are best suited tooperation on land and with relatively small through-puts. So far as theinventor is at present aware, no recovery and separation system for oiland water has been previously proposed specifically for use at sea andproved successful. A major problem is the paradoxical requirement thatan antipollution vessel working in a heavily polluted sea is itselfbound by the oil discharge regulations not to discharge into the seawater which contains significant quantities of oil. The need, therefore,which has not previously been satisfied, so far as the present inventoris aware, is for a system which is both relatively quick and effectivein separating oil and water.

DESCRIPTION OF THE INVENTION

The invention provides, in a first aspect, apparatus for the removal andrecovery of pollutant oil and the like floating on the surface of a bodyof water, comprising: means capable of the physical withdrawal ofpollutant oil and the like with or without additional water from thewater surface to a recovery station on site; means for spraying hotwater over such pollutant oil and the like at said recovery station; areceiving tank for the oil/water washings resulting; an oil/waterseparator/coalescer for separating oil containing a minor quantity ofwater only from the washings; means for receiving such separated oil;means for recirculating water from said separator/coalescer for heatingand further spraying; and means for returning any excess purified waterfrom said separator/coalescer to said body of water.

In a second aspect, the present invention provides a method for theremoval and recovery of oil floating on the surface of a body of water,which method comprises the steps of: the physical withdrawal ofpollutant oil and the like with or without additional water from thewater surface to a recovery station on site; spraying hot water oversuch pollutant oil and the like at said recovery station; receiving theoil/water washings resulting: separating oil containing only a minorquantity of water from the washings; re-circulating water from which oilhas been separated for heating and further spraying; and returning anyexcess purified water to said body of water.

The term "pollutant oil and the like" is used herein to encompass one ormore of oil, including heavy crude oil or heavier tarry constituents ofoil, oil/water mousse, and other petroleum of liquid fuel basedproducts, liable to pollute bodies of water whether inadvertantly or byillegal or antisocial design.

The receiving station is suitably a floating vessel. Theseparator/coalescer is preferably a corrugated plate separator. A pumpis provided for the recirculation of water and the system is preferablycontrolled by a microprocessor linked to an oil content monitor in therecirculation stream.

Numerous means are known for physically withdrawing oil and/or oil/watermousse from water surfaces and the present invention may be practicedwith any such known physical or mechanical arrangements. In particular,the present invention may be employed with scoops, sweeping boomarrangements, vacuum arrangements, etc. The present invention is notlimited to any particular such arrangement but is generally applicable.

The invention is hereinafter more particularly described by way ofexample only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view through an apparatusconstructed in accordance with the present invention mounted on and froma ship.

FIG. 2 is a view of the physical withdrawal means of the apparatus ofFIG. 1 seen from above.

FIG. 3 is a sectional view taken along the line III--III in FIG. 2.

FIG. 4 shows a small section of the physical withdrawal means shown inFIGS. 1 to 3.

FIGS. 5A, 5B and 5C schematically illustrate the manner in which oil iswithdrawn from the sea in the apparatus of FIGS. 1 to 4.

FIG. 6 schematically illustrates the microprocessor control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show one form of mechanical arrangement for removing oilfrom the surface of the sea and bringing it on board a vessel. Thearrangement here shown is, I believe, itself novel, and is described inand is the subject of British patent application No. 49121/78 andBritish patent application No. 43787/79 which claims priority from49121/78. An endless belt 1 formed of expandible mesh material, andhaving oleophilic properties, is supported on a series of pontoons 2floating on the surface of the sea, on a support 4 rising from the seasurface, and on a shipborne support section 5. Drive 6 for the belt 1 isprovided at the inboard side of section 5.

The preferred construction for the belt is shown in FIG. 3 in section.It will be seen that the belt is of compound construction including anumber of component layers 7 with various size mesh to thereby collect(as will be explained below) a broad range of oil droplet sizes. Thelayers 7 are sandwiched between outer layers of a heavy support mesh 8.The edges of the belt are formed by heat bonding and by inserting aseries of eyelets 9. Also shown in section in FIG. 3 is one guidebox 10.A similar guidebox would be provided for the other side of the belt. Theguide-boxes extend along the respective edges of the support 2, 4 and 5.Within the guide-boxes run respective drive chains 11 provided withupstanding pins 12 at sections therealong for coaction with theapertures defined by the eyelets 9. The several pontoons 2 and therising section 4 all have the same lateral width which is chosen so thatthe mesh is in a relatively unexpanded condition (as shown in FIG. 4).The length to width ratio for respective mesh cells in this natural,unstressed condition may be of the order of 8:1. As is best shown inFIG. 2, section 5 broadens out from its junction with the rising section4 to its inboard end. Thus, as the belt travels along the section 5towards the inboard end, the mesh is steadily expanded laterally by thedrive chains 11 and pins 12 pulling the respective longitudinal edges ofthe mesh. In the fully "open" conditions, each mesh cell may have alength to width ratio of approximately 1:1.

The material of the expandible mesh is preferably itself oleophilic. Asuitable material is polypropylene. Expandible polypropylene meshmaterial is readily available for example from Netlon Limited. The mesh(whether itself oleophilic or not) is suitably (though not necessarilyif the material is itself oleophilic) provided with an oleophiliccoating. Thus, the most preferred mesh is formed of polypropylene and istreated with a silicone coating which is cured thereon.

Since the mesh material is oleophilic, oil floating in the surfaceregions of the sea 3 will tend to be attracted to the mesh, and will bepicked up by the belt. Fine discrete droplets of oil will tend to adhereto the surface of the mesh material, as shown at 13 in FIG. 5A. Motionof the belts themselves, aided by wave motion, will tend to move theindividual droplets along the strands of mesh material, so increasingthe chance of coalescence of these droplets 13 into larger droplets. Theoleophilic nature of the mesh material together with surface tensioneffects will provide a "bridging" effect in the voids in the mesh cellsso that somewhat larger droplets or larger quantities of oil will tendto adhere to the mesh as shown at 14 in FIG. 5B. Larger lumps of oil orsemi-solid oil/water mousse will tend to be physically lifted out of thewater by the moving belt as shown at 15 in FIG. 5C. As the processcontinues and the belt progresses from the sea on board the ship,coalescence between oil carried in any of the manners 13, 14 or 15 willtend to occur. By forming the belt with a compound construction asdescribed above with reference to FIG. 3, droplets of different sizeswill find a mesh size best suited for retaining same, so that the effectof employing a compound belt is to increase the quantity of oil whichwill be picked up and also to ensure that the apparatus will workeffectively over a broad range of conditions which might be found inpractice at sea.

At all events, as described above, when the belt reaches the supportsection 5, the mesh will be steadily expanded laterally to "open" themesh cells. As will be appreciated, this facilitates detachment of oilcarried by the belt. Indeed, drops such as that shown at 14 in FIG. 5Bmay simply fall through the space in the mesh into receiving tank 16.

The system consisting of the belt 1, the floating pontoon support 2, therising section 4, and the inboard support section 5 has been describedin detail hereinabove since it is a means of this kind which I currentlyprefer to employ for the physical withdrawal of oil and/or oil/watermousse from the surface of the sea on board the recovery vessel. For amore detailed description of modified versions of this apparatus thereader is referred to British patent application No. 43787/79 mentionedabove. The processing means, whereby oil containing minor quantitiesonly of water (as little as, say, 5% or less) is recovered and storedwill be described in detail below. It will be appreciated that suchspearation, recovery and storage system, which forms means, relating toan essential element of the invention, for putting that invention intoeffect may be employed with other embodiments of physical withdrawalmeans.

For example, a solid belt skimmer arrangement is available from RexnordInc., and could be used with the recovery system. Again, a rope skimmerarangement known under the trade name "Oil Mop" could also be used. Inthis latter arrangement, a multi-strand rope is placed in the sea tosuck up oil preferentially, is withdrawn on board and is squeezed orcompressed to physically remove oil (together with some water) adheringto the rope. Other arrangements involving scoops, moving booms, paddlearrangements rotating about a vertical axis and coupled to a suctionline, etc. may equally well be employed.

In any event, pollutant oil and the like (that is to say: oil, and/oroil/water mousse, etc.) with or without additional water is withdrawnfrom the water surface to a recovery station on site, which in the caseof oil recovery at sea will be a floating vessel. Hot water is sprayedover such oil and/or oil/water mousse, etc. at the recovery station andthe washings are received in a tank. In the particular arrangementillustrated, hot water is sprayed over support section 5 from aplurality of nozzles 17 and aids in physical detachment of oil dropletsfrom the belt. The water is heated as, for example, by means of a heatexchanger 18 which may derive heat from the steam heating system of theship. The majority of small droplets 13 and drops 14 will tend either tofall through the spaces in the mesh or to be stripped from the belt bythe hot water spray. Large lumps of semi-solid oil/water mousse not sodetached will tend to fall off the belt when the belt starts its returnrun and to fall into the hot water washings. The hot water tends tobreak up the large oil lumps. The water washings together with anyoil/water lumps are received in a tank 16 and are subjected toseparation, the hot water already having broken up the large oil lumpsto some extent. Any suitable separator and/or coalescer system may beemployed, but that which I prefer is a corrugated plate separator 19 ofthe kind manufactured by Fram Europe Limited. Such a separator allowsoil containing a minor quantity of water only (as little, say, as 5%water) to be withdrawn from the tank by means of an oil skimmer 21. Theremaining water containing only minor quantities of remaining oil isused being pumped by means of a pump 22 from the bottom of the tank viaan oil content monitor 23 to the heat exchanger 18. As the watercirculatory system is essentially closed, heating may be accomplishedwith a relatively low expenditure of energy. Some sea water may becarried on board the vessel even when the preferred belt arrangement isemployed. With other forms of physical withdrawal means rather more seawater may be brought on board. An excess of water will thus tendgradually to accumulate in the system. Such excess water may bedischarged to sea automatically from the system at a position betweenthe oil content monitor and the heat exchanger, though in this case, themonitored oil content in the water must be sufficiently low to meet theoil discharge regulations.

The efficiency of the oil removal and the oil/water separating systemsare affected by many variables, including, but not limited to, oil typeand condition, sea temperature, oil slick thickness, mesh belt speed,vessel speed, wave motion, wash water temperature, wash water flow, andwash water contamination. All of these variables affect the efficiencyof the removal and separation systems singularly and in interaction witheach other.

The microprocessor control circuit of FIG. 6, using conventional digitalcomputing techniques is employed to simultaneously receive input datafrom a plurality of sensors indicative of the said efficiency affectingvariables and to process such data singularly and in interaction witheach other in accordance with a pre-set program to optimise theefficiency of the system over a wide range of operation conditions.

In particular the flow rate of water in the system is adjusted byregulation of pump 22 in accordance with the residual oil content signalprovided by monitor 23 so as to achieve a sufficiently low oil contentin the efflux water irrespective of varying oil concentrations receivedin tank 6.

In general, it is preferred to employ the following sensors to provideinput data to the microprocessor:

1. Temperature sensors in the sea water and in the wash water;

2. Capacitance or resistance probes placed immediately ahead of thedistal pontoon section to sense oil slick thickness;

3. Tachometers attached to the mesh belt drive and the wash water pumpto provide belt speed and water flow data;

4. Rotational sensors fitted to the hinge points between pontoonsections to provide data on wave height and period;

5. A signal from the ship's log proportional to vessel speed through thewater; and

6. A signal from the oil content monitor 23 proportional to the amountof oil remaining in the wash water.

Certain data is manually entered into the microprocessor at the start ofa pollutant oil recovery operation. Such data includes:

(a) Oil type;

(b) Oil viscosity;

(c) Oil specific gravity;

(d) Length of time that oil has been in contact with water;

(e) Minimum and maximum temperatures that oil water mixture has beenexposed to since the spill;

(f) Oceanagraphic data; and

(g) Bulk density of sea water.

From this manually entered data, the optimum separation characteristics,the most probable oil droplet size distribution and the mousse conditioncan be computed.

Static data manually entered and dynamic data from the various sensorsis processed in accordance with the preset program to provide controlsignals to controllable components, which may include:

(a) Angle setting means for controlling the depth of the pontoonsections;

(b) Belt drive motor 6 to optimise oil load on the belt;

(c) Hydraulic dampers at pontoon section hinge points to provide optimumwave following characteristics by changing the natural frequency anddamping factors of the pontoon sections;

(d) Flow and temperature of the wash water to optimise separationefficiency and the breakdown of "mousse"; and

(e) A visual indication of optimum ships speed to the helmsman.

For example, the detection of a very thick slick of high specificgravity oil that had been in cold water for many days would signal theangle-setting means to position the "nose" of the distal pontoon sectiondeep into the oil/water interface and speed up the belt drive 6 tomaximise the belt loading whilst signalling the ship to slow down if theoil slick thickness and condition indicated more oil than the belt couldhandle. The oil type and condition data manually entered would havecomputed the correct wash water temperature to optimise the meshcleaning, oil separation and mousse breakdown capabilities.

The data from the oil content monitor is used to "fine tune" ship speed,belt speed and water flow by conventional negative feed-back techniquesto maximise pick-up rate by optimising separator efficiency.

While the invention has largely been described with reference to theillustrated expandible mesh belt arrangement for the mechanical removalof pollutant oil and the like from the surface of a body of water, theteachings herein may equally well be applied, with appropriatemodifications and adaptations which will readily occur to the manskilled in this art, to other forms of physical withdrawal of pollutantoil and the like from water surfaces.

What is claimed is:
 1. Apparatus for the removal and recovery ofpollutant oil and the like floating on the surface of a body of water,comprising:recovery means for withdrawing pollutant oil and the likewith possible additional water from the water surface and carrying it toa recovery station, said recovery means comprising an endless beltformed of expandable mesh material, and having oleophilic properties,which belt is disposed to pass round a plurality of pontoon sectionsfloating at or adjacent the water surface and then out of the water tosaid recovery station, means for removing the pollutant oil and the likeincluding means for spraying hot water over said recovery means toremove such pollutant oil and the like at said recovery station andmeans for expanding the mesh of the belt in a direction at right anglesto the direction of movement thereof to faciliate detachment ofpollutant oil and the like from said belt by said hot water spray; areceiving tank for receiving the oil/water washings resulting from saidmeans for removing; an oil/water separator/coalescer for separating oilcontaining only a minor quantity of water from the washings; means forreceiving such separated oil; means for recirculating water from saidseparator/coalescer and directing said recirculated water to a heatingmeans and then to said means for spraying; and means for returning anyexcess purified water from said separator/coalescer to said body ofwater.
 2. Apparatus according to claim 1, wherein the receiving stationis a floating vessel and wherein said apparatus is mounted on and fromsaid vessel, separated oil being stored in the vessel's hold. 3.Apparatus according to claim 1, further comprising an oil contentmonitor adapted to monitor residual oil content in the recirculatedwater and arranged to generate a control signal for controlling saidexcess water return means to allow discharge of excess water only whensaid residual oil content is below a predetermined level.
 4. Apparatusaccording to claim 1, wherein said separator/coalescer comprises aparallel plate separator.
 5. A method for the removal and recovery ofpollutant oil and the like floating on the surface of a body of water,which method comprises the steps of:withdrawing pollutant oil and thelike from the water surface by passing an endless belt formed ofexpandible mesh material, and having oleophilic properties, round aplurality of pontoon sections floating at or adjacent the water surfaceand then out of the water to a recovery station; spraying hot water oversaid recovery means to remove such pollutant oil and the like at saidrecovery station; receiving the oil/water washings resulting; separatingoil containing only a minor quantity of water from the washings;recirculating water from which oil has been separated for heating andfurther spraying; and returning any excess purified water to said bodyof water.
 6. A method according to claim 5, wherein the residual oilcontent of said recirculated water is monitored and return discharge ofexcess water is controlled in accordance therewith.
 7. A methodaccording to claim 5,wherein said method is performed at sea under thecontrol of a microprocessor receiving variable input data relating toone or more of the temperature of the sea water and of the said hotwater, to oil slick thickness, to belt speed and hot water flow rate, towave height and period, to ship's speed through the water; and whereinthe residual oil content of said recirculated water is monitored toprovide a further variable input for said microprocessor; themicroprocessor being preset with data relating to one or more of: oiltype, oil viscosity, oil specific gravity, length of time the oil hasbeen in the sea, minimum and maximum ambient temperatures to which ithas been exposed since spilling into the sea, oceanographic data, andthe bulk density of the sea water; and the microprocessor providingcontrol signals for controlling one or more of: the speed of said beltto optimise oil load thereon, said angle setting means to select saidleading angle, hydraulic dampers at hinge points between pontoonsections to provide optimum wave following profiles, and flow rate andtemperature of said heated water, and optionally for providing a visualindication to the helmsman of optimum ship's speed.